Hello my F250 heater/defroster just stays in the defrost position no matter what you select it on the dash board. It will go off when set to the off position when selected off. Select the foot position and just the defrost comes on,select the air to come out of the vents and still just the defrost comes on. Any ideas?? thanks john

 

Sounds like you have a vacuum leak. Check under the glove box on the passenger side, and in the engine compartment near the vacuum pump.

Under the glove box:
Inspect these black and white tubes. Somewhere along the line the layout was changed. Mine is the updated one. Earlier model had an issue with passengers confidently kicking these. I also have a kick plate that covers these to prevent that. But that was also added to help prevent people from kicking these.


Under hood:
Trace all vacuum lines and check for a disconnected line.

 

Thanks for the detailed info. I will try to check tomorrow in the light!...john

 

Information i found on vacuum pumps for the F250 diesel.....Your heater defaults to defrost only, and your four wheel drive may not engage if the pump does not run at all. The pump may also fail and run continuously - in this case, there may be a leak in the system which the vacuum pump can not keep up with, so it runs all the time. Disconnect the outlet hose and plug the connection on the pump with your finger. If the pump stops running there is a leak in the system - probably a broken line, etc. If the pump does not stop running when you perform this test, it is bad and needs replacement.

 

I'm having the same issue and need some advice. The solenoid never closes. I've tested it. The vacuum line running to the hubs pressurizes and then steadily drops. Is this normail and if not what should the reading be? What's the best way to find exactly where the leak is? And who the hell decided to run the lines on the bottom front of the engine????

 

Welcome Wendy. What year truck are you working on? Can you hear the vacuum pump run? You say the line running to the hubs pressurizes, then pressure drops. How are you measuring this?

If you were to disconnect the line going to the hubs near the vac reservoir/PVHS(solenoid) and test, does the vacuum hold?

 

Look for a leaky PVH solenoid if you have 4x4.